Field of the Invention
The present invention relates to the diagnosis or the prognosis of metastasis in prostate cancer based on determining if the c-MAF gene, within the 16q22-24 genomic region, is amplified in a primary tumor sample. Likewise, the invention also relates to a method for the diagnosis or the prognosis of metastasis in prostate cancer, as well as to a method for designing a customized therapy in a subject with prostate cancer, which comprises determining the c-MAF gene expression level or 16q22-24 amplification. Finally, the invention relates to the use of a c-MAF inhibitor as a therapeutic target for the treatment of prostate cancer metastasis.
Background Art
The Problem:
Metastasis, a complex process caused by elaborate interactions between tumor cells and the surrounding normal tissues in different vital organs, accounts for 90 percent of all cancer deaths in patients with solid tumors. The molecular and cellular mechanisms that lead primary tumors to form metastases must be understood in order to better address this major life-threatening problem. The identification of metastasis genes and mechanisms is essential for understanding the basic biology of this lethal condition and its implications for clinical practice.
Introduction and Interest: Prostate Organ-specific Metastasis
Prostate cancer is a form of cancer that develops in the prostate, a gland in the male reproductive system. Most prostate cancers are slow growing; however, there are cases of aggressive prostate cancers. The cancer cells may metastasize (spread) from the prostate to other parts of the body, particularly the bones and lymph nodes. Prostate cancer may cause pain, difficulty in urinating, problems during sexual intercourse, or erectile dysfunction. Other symptoms can potentially develop during later stages of the disease.
Rates of detection of prostate cancers vary widely across the world, with South and East Asia detecting less frequently than in Europe, and especially the United States. Prostate cancer tends to develop in men over the age of fifty and although it is one of the most prevalent types of cancer in men, many never have symptoms, undergo no therapy, and eventually die of other causes. About two-thirds of cases are slow growing, the other third more aggressive and fast developing.
Many factors, including genetics and diet, have been implicated in the development of prostate cancer. The presence of prostate cancer may be indicated by symptoms, physical examination, prostate-specific antigen (PSA), or biopsy. The PSA test increases cancer detection but does not decrease mortality. Moreover, prostate test screening is controversial at the moment and may lead to unnecessary, even harmful, consequences in some patients. Nonetheless, suspected prostate cancer is typically confirmed by taking a biopsy of the prostate and examining it under a microscope. Further tests, such as CT scans and bone scans, may be performed to determine whether prostate cancer has spread.
Management strategies for prostate cancer should be guided by the severity of the disease. Many low-risk tumors can be safely followed with active surveillance. Curative treatment generally involves surgery, various forms of radiation therapy, or, less commonly, cryosurgery; hormonal therapy and chemotherapy are generally reserved for cases of advanced disease (although hormonal therapy may be given with radiation in some cases).
The age and underlying health of the man, the extent of metastasis, appearance under the microscope and response of the cancer to initial treatment are important in determining the outcome of the disease. The decision whether or not to treat localized prostate cancer (a tumor that is contained within the prostate) with curative intent is a patient trade-off between the expected beneficial and harmful effects in terms of patient survival and quality of life.
The specific causes of prostate cancer remain unknown. Genetic background may contribute to prostate cancer risk, as suggested by associations with race, family, and specific gene variants. No single gene is responsible for prostate cancer; many different genes have been implicated. Mutations in BRCA1 and BRCA2, important risk factors for ovarian cancer and breast cancer in women, have also been implicated in prostate cancer. Other linked genes include the Hereditary Prostate cancer gene 1 (HPC1), the androgen receptor, and the vitamin D receptor. TMPRSS2-ETS gene family fusion, specifically TMPRSS2-ERG or TMPRSS2-ETV1/4 promotes cancer cell growth.
Loss of cancer suppressor genes, early in the prostatic carcinogenesis, have been localized to chromosomes 8p, 10q, 13q, and 16q. P53 mutations in the primary prostate cancer are relatively low and are more frequently seen in metastatic settings, hence, p53 mutations are a late event in pathology of prostate cancer. Other tumor suppressor genes that are thought to play a role in prostate cancer include PTEN (gene) and KAI1. Up to 70 percent of men with prostate cancer have lost one copy of the PTEN gene at the time of diagnosis. Relative frequency of loss of E-cadherin and CD44 has also been observed.
Prostate cancer is classified as an adenocarcinoma, or glandular cancer, that begins when normal semen-secreting prostate gland cells mutate into cancer cells. The region of prostate gland where the adenocarcinoma is most common is the peripheral zone. Initially, small clumps of cancer cells remain confined to otherwise normal prostate glands, a condition known as carcinoma in situ or prostatic intraepithelial neoplasia (PIN). Although there is no proof that PIN is a cancer precursor, it is closely associated with cancer. Over time, these cancer cells begin to multiply and spread to the surrounding prostate tissue (the stroma) forming a tumor. Eventually, the tumor may grow large enough to invade nearby organs such as the seminal vesicles or the rectum, or the tumor cells may develop the ability to travel in the bloodstream and lymphatic system. Prostate cancer is considered a malignant tumor because it is a mass of cells that can invade other parts of the body. This invasion of other organs is called metastasis. Prostate cancer most commonly metastasizes to the bones, lymph nodes, and may invade rectum, bladder and lower ureters after local progression.
Molecular Traits of Prostate Cancer
RUNX2 is a transcription factor that prevents cancer cells from undergoing apoptosis thereby contributing to the development of prostate cancer.
The PI3k/Akt signaling cascade works with the transforming growth factor beta/SMAD signaling cascade to ensure prostate cancer cell survival and protection against apoptosis. X-linked inhibitor of apoptosis (XIAP) is hypothesized to promote prostate cancer cell survival and growth and is a target of research because if this inhibitor can be shut down then the apoptosis cascade can carry on its function in preventing cancer cell proliferation. Macrophage inhibitory cytokine-1 (MIC-1) stimulates the focal adhesion kinase (FAK) signaling pathway which leads to prostate cancer cell growth and survival.
The androgen receptor helps prostate cancer cells to survive and is a target for many anti-cancer research studies; so far, inhibiting the androgen receptor has only proven to be effective in mouse studies. Prostate specific membrane antigen (PSMA) stimulates the development of prostate cancer by increasing folate levels for the cancer cells to use to survive and grow; PSMA increases available folates for use by hydrolyzing glutamated folates.
Diagnosis
The only test that can fully confirm the diagnosis of prostate cancer is a biopsy, the removal of small pieces of the prostate for microscopic examination. However, prior to a biopsy, less invasive testing can be conducted.
There are also several other tests that can be used to gather more information about the prostate and the urinary tract. Digital rectal examination (DRE) may allow a doctor to detect prostate abnormalities. Cystoscopy shows the urinary tract from inside the bladder, using a thin, flexible camera tube inserted down the urethra. Transrectal ultrasonography creates a picture of the prostate using sound waves from a probe in the rectum.
Prostate Imaging
Ultrasound (US) and Magnetic Resonance Imaging (MRI) are the two main imaging methods used for prostate cancer detection.
Biopsy
Micrograph showing a prostate cancer (conventional adenocarcinoma) with perineural invasion. H&E stain.
If cancer is suspected, a biopsy is offered expediently. During a biopsy a urologist or radiologist obtains tissue samples from the prostate via the rectum. A biopsy gun inserts and removes special hollow-core needles (usually three to six on each side of the prostate) in less than a second. Prostate biopsies are routinely done on an outpatient basis and rarely require hospitalization. Fifty-five percent of men report discomfort during prostate biopsy.
Gleason Score
The tissue samples are then examined under a microscope to determine whether cancer cells are present, and to evaluate the microscopic features (or Gleason score) of any cancer found. Prostate specific membrane antigen is a transmembrane carboxypeptidase and exhibits folate hydrolase activity. This protein is overexpressed in prostate cancer tissues and is associated with a higher Gleason score.
Tumor Markers
Tissue samples can be stained for the presence of PSA and other tumor markers in order to determine the origin of malignant cells that have metastasized.
Small cell carcinoma is a very rare (1%) type of prostate cancer that cannot be diagnosed using the PSA. As of 2009 researchers are trying to determine the best way to screen for this type of prostate cancer because it is a relatively unknown and rare type of prostate cancer but very serious and quick to spread to other parts of the body. Possible methods include chromatographic separation methods by mass spectrometry, or protein capturing by immunoassays or immunized antibodies. The test method will involve quantifying the amount of the biomarker PCI, with reference to the Gleason Score. Not only is this test quick, it is also sensitive. It can detect patients in the diagnostic grey zone, particularly those with a serum free to total Prostate Specific Antigen ratio of 10-20%.
The expression of Ki-67 by immunohistochemistry may be a significant predictor of patient outcome for men with prostate cancer.
Classification
An important part of evaluating prostate cancer is determining the stage, or how far the cancer has spread. Knowing the stage helps define prognosis and is useful when selecting therapies. The most common system is the four-stage TNM system (abbreviated from Tumor/Nodes/Metastases). Its components include the size of the tumor, the number of involved lymph nodes, and the presence of any other metastases.
The most important distinction made by any staging system is whether or not the cancer is still confined to the prostate. In the TNM system, clinical T1 and T2 cancers are found only in the prostate, while T3 and T4 cancers have spread elsewhere. Several tests can be used to look for evidence of spread. These include computed tomography to evaluate spread within the pelvis, bone scans to look for spread to the bones, and endorectal coil magnetic resonance imaging to closely evaluate the prostatic capsule and the seminal vesicles. Bone scans should reveal osteoblastic appearance due to increased bone density in the areas of bone metastasis-opposite to what is found in many other cancers that metastasize.
After a prostate biopsy, a pathologist looks at the samples under a microscope. If cancer is present, the pathologist reports the grade of the tumor. The grade tells how much the tumor tissue differs from normal prostate tissue and suggests how fast the tumor is likely to grow. The Gleason system is used to grade prostate tumors from 2 to 10, where a Gleason score of 10 indicates the most abnormalities. The pathologist assigns a number from 1 to 5 for the most common pattern observed under the microscope, then does the same for the second-most-common pattern. The sum of these two numbers is the Gleason score. The Whitmore-Jewett stage is another method sometimes used.
Screening
Prostate cancer screening is an attempt to find unsuspected cancers, and may lead to more specific follow-up tests such as a biopsy, with cell samples taken for closer study. Options include the digital rectal exam (DRE) and the prostate-specific antigen (PSA) blood test. Such screening is controversial and, in some patients, may lead to unnecessary, even harmful, consequences. A 2010 analysis concluded that routine screening with either a DRE or PSA is not supported by the evidence as there is no mortality benefit from screening. More recently, the United States Preventive Services Task Force (USPSTF) recommended against the PSA test for prostate cancer screening in healthy men. This USPSTF recommendation, released in October 2011, is based on “review of evidence” studies concluding that “Prostate-specific antigen-based screening results in small or no reduction in prostate cancer-specific mortality and is associated with harms related to subsequent evaluation and treatments, some of which may be unnecessary.
Modern screening tests have found cancers that might never have developed into serious disease, and that “the slight reduction of risk by surgically removing the prostate or treating it with radiation may not outweigh the substantial side effects of these treatments,” an opinion also shared by the CDC.
Aggressive Cancer
If the cancer has spread beyond the prostate, treatment options significantly change, so most doctors that treat prostate cancer use a variety of nomograms to predict the probability of spread. Treatment by watchful waiting/active surveillance, external beam radiation therapy, brachytherapy, cryosurgery, HIFU, and surgery are, in general, offered to men whose cancer remains within the prostate. Hormonal therapy and chemotherapy are often reserved for disease that has spread beyond the prostate. However, there are exceptions: radiation therapy may be used for some advanced tumors, and hormonal therapy is used for some early stage tumors. Cryotherapy (the process of freezing the tumor), hormonal therapy, and chemotherapy may also be offered if initial treatment fails and the cancer progresses.
If the disease has reached clinical stage T3 or T4, it is classified as advanced prostate cancer. Advanced prostate cancer with bone metastasis or lymph node metastasis is more likely to cause Prostate Cancer Symptoms than is an early stage of the disease. Doctors usually check for bone metastasis and lymph node metastasis which are denoted respectively by M and N in clinical staging.
In clinical stage T3, the tumor has extended beyond the prostatic capsule, possibly into the seminal vesicles, and is specifically called extraprostatic extension. Extraprostatic means “independent of the prostate gland.” In clinical stage T4, the disease invades surrounding organs (other than the seminal vesicles) such as the bladder neck, external sphincter, or rectum.
Metastasis is more likely to occur during advanced prostate cancer. Metastatic disease refers to prostate cancer that has left the prostate gland and its neighboring organs. Advanced prostate cancer bone metastasis and lymph node metastasis, which can be local or distant, are both associated with advanced prostate cancer. Metastases may involve symptoms that are not in the Prostate Cancer Treatment Guide.
Prostate Cancer Lymph Node Metatastis The body produces a fluid called lymph which contains white blood cells and circulates through the lymphatic system. Lymph nodes are small oval or circular organs that filter this fluid. Cancerous cells that circulate through the body can become trapped in the lymph nodes. Once trapped, cancerous cells can begin their cycle of unhealthy division and result in lymph node metastasis.
There are two types of lymph node metastasis: local and distant. Local lymph node metastasis is designated by clinical stage N1. Two lymph nodes lie on either side of the bladder. Because these nodes are close to the prostate gland, metastasis is considered local. If cancerous cells begin to grow in any other lymph node, the metastasis is considered distant. Distant lymph node metastasis is denoted by clinical stage M1a.
Prostate Cancer Bone Metastasis Primary cases of bone cancer are relatively rare. Patients who develop bone cancer are more likely to develop the disease as a result of advanced prostate cancer metastasis. In prostate cancer, extension leading to bone disease is designated by a clinical stage M1b. If a person develops bone disease as a result of prostate cancer, he does not now have bone cancer. Because the cancer is classified according to where it originated, he has prostate cancer with bone metastasis.
Skeletal metastases occur in more than 80% of advanced-stage prostate cancer and they confer a high level of morbidity, a 5-year survival rate of 25% and median survival of approximately 40 months. Of the estimated one million annual deaths associated with metastatic bone disease in the USA, EU and Japan, approximately 20% are cases of advanced-stage prostate cancer. Treatment-naïve metastatic prostate cancer is largely sensitive to androgen-deprivation therapy but progression to castration-resistant prostate cancer occurs 18-20 months after starting treatment. Metastatic bone disease causes some of the most distressing symptoms of advanced-stage cancer; estimates indicate that treatment of bone pain is required in approximately 30% of men with castration resistant prostate cancer and associated with metastatic bone disease; with 22% requiring treatment for singular or multiple pathological skeletal fractures; 7% for spinal-cord compression; 3-4% for hemiparesis or paresis. At first diagnosis of bone metastasis disease therapeutic intervention will usually involve systemic chemotherapy, hormonal therapy and bisphophonates or Denosumab, which are mostly palliative options with the intention of reducing pain.
In healthy skeletal bone, an equal balance of new bone matrix formation and old bone matrix resorption is achieved via coordinated activity of bone-degrading osteoclasts and bone-forming osteoblasts. During metastasis bone disease, the normal balance of bone resorption and formation is disrupted by the homotypic and heterotypic cell-cell interactions that occur between invading tumor cells, osteoblasts and ostoclasts. Most patients with secondary bone tumors—including those associated with castration resistant prostate cancer-present with osteolytic lesions. Therefore, most treatment strategies in current use or under evaluation in metastatic bone disease have been designed to protect the bone matrix from increased bone degrading activity of osteoclasts. An additional complication that presents in more than 80% of men with castration-resistant prostate cancer and metastasis bone disease are osteosclerotic lesions—also known as bone-forming or osteoblastic lesions—or a combination of both, osteolytic and osteosclerotic lesions—also referred to as mixed lesions. Osteosclerotic lesions are typified by bone deposits with multiple layers of poorly organized type-I collagen fibrils that have a woven appearance and reduced mechanical strength.
Prostate cancer cells preserve, among each subtype, genome-aberration-induced transcriptional changes with high fidelity. The resulting dominant genes reveal molecular events that predict the metastatic outcome despite the existence of substantial genomic, transcriptional, translational, and biological heterogeneity in the overall system. However, it is unknown whether the developmental history of a cancer would result in different or common mediators of site-specific metastasis. Predisposing factors related to the cell of origin may engender different rate-limiting barriers during metastasic progression. Herein, we proposed the use of a new biomarker as a prognostic factor in primary tumors that predicts future bone metastasis events. Moreover, we also propose the use of this gene as a potential therapeutic target to prevent, stop and cure prostate cancer derived bone metastasis.